1. Field of the Invention
The present invention relates to belting, and, more particularly, to belting having improved dimensional stability characteristics. Belting in accordance with the present invention is particularly useful in agricultural applications, e.g., in hay balers, where environmental and loading conditions can be severe.
2. Description of the Prior Art
Belting is used today in many types of agricultural machinery, e.g., hay balers. A popular type of hay baler which is marketed today employs a plurality of belts which are used to form the hay into round bales. This type of baler is known as a round hay baler, and the belts which are used on round hay balers are typically on the order of forty feet in length.
There are several factors which must be taken into consideration when designing belting for hay balers. One factor is that, when a hay baler is making bales, the belts are subjected to heavy loads. These loads cause the belts to stretch, and the amount that a belt stretches under load must remain with a certain tolerance or the bale it is making will become too large, which interferes with proper baler operation.
The amount of stretch in belts used on hay balers is not insignificant. For example, a typical maximum specification for elongation of belts for hay balers has been three percent at a specified load. A forty foot belt is thus permitted to stretch up to about fourteen inches under that load. When the belt stretches beyond tolerable limits, the belt is removed and shortened. Shortening of the belt is typically accomplished by trial and error techniques, especially in the field. Such trial and error techniques can produce unsatisfactory results.
Manufacturers of hay balers have continued to increase the specification for the density of bales which a baler can produce. The amount of loading to which the belts of the baler are subjected to make denser bales is increased, and hence the likelihood that a belt will stretch by an amount beyond tolerable limits for proper operation is increased.
Another factor to be considered in belt design is the ability of the belt to flex in operation without the ply material cracking. In that regard, a typical round hay baler employs a plurality of rollers on which the belts are installed. The position of the rollers is such that the belts are subjected to substantial amount of flexing in travelling around the rollers. Moreover, some of the rollers are positioned such that the belts must travel in an S-shape during operation. If the belts fail due to the flexing stress, the belt must be replaced to obtain proper operation of the baler.
Another aspect of the flexing problem is manifested at the location where a belt is spliced. A popular way to connect the ends of a belt is with the so-called "clipper splice" as shown in FIG. 3. The likelihood of belt failure due to flexing is most pronounced at the location in the belt in the vicinity of the clipper splice. This is because the plies of the belts are most prone to crack at the splice.
Yet a third factor which must be considered in belt design is the environment in which the belting is used. Belts used on agricultural equipment are subjected to severe environmental condition, and, in this regard, moisture is perhaps the greatest problem. If the ply material of the belting is deteriorated by moisture, the belt can fail in operation.
It is seen that belting for hay balers need to be dimensionally stable, able to flex without cracking, and not subject to environmental deterioration.
Heretofore, a popular belt which has been used on hay balers is a two-ply belt, wherein the plies are made of a polyamide fabric, e.g., Nylon*. Polyamide fabrics are used in belts for hay balers, inasmuch as they have excellent flexing characteristics and are not as susceptible to moisture deterioration as other types of materials. However, the elongation problems in such belts is pronounced, since a polyamide material has a relatively high elongation modulus and also tends to stretch when wet. FNT *Nylon is believed to be a registered mark of DuPont.
One proposed solution to the elongation problem in two-ply polyamide belts has been to initially make the belt shorter than required in order to compensate for the elongation. Under this proposed solution, the assumption is that all the belts will stretch in use to the proper length. This approach is not really sound or acceptable, since all belts on the hay baler do not stretch an exact amount. Even though unacceptable, this approach has been utilized in the industry to accept for the elongation problem, and at the present time, the standard of the industry has been two-ply polyamide belting.
There have been other suggestions to solve the elongation or stretching problem in belts. One such suggestion was to make a two-ply belt, where the plies were made of a rayon material. Rayon has a lower elongation modulus than a polyamide fabric, and, hence, does not stretch as much as a polyamide belt under the same load. However, this belt proved to be unacceptable, since rayon is particularly susceptible to moisture attack.
Another suggestion for solving the elongation problem was to make a two-ply belt wherein the plies were made of a polyester material. This proposed solution was ineffective inasmuch as the polyester plies tended to crack when flexed, and the cracking was most pronounced in the area of the clipper splice.
Another type of belting which was used on hay balers included a three-ply belt wherein the center ply was made of polyamide fabric, and wherein the two outer plies were made of cotton. This type of belt failed, inasmuch as moisture caused the cotton to rot and the belt then failed, since it was not able to carry a sufficient load.
No belting has been heretofore available which: (1) exhibits good dimensional stability characteristics; (2) is not subject to deterioration based on environmental conditions; and (3) can withstand the flexing requirements imposed on belts by hay balers.